DCTF, chemical name 2,3-dichloro-5-(trifluoromethyl) pyridine, CAS No. 69045-84-7, is a colorless and transparent liquid with relative density of 1.55 (water is 1.0) under room temperature. As an important pesticide and medicine intermediate, DCTF can not only be used for production of fluoric herbicide such as fluazifop-butyl, haloxyfop-ethoxyethyl and haloxyfop, but also be widely applied in production of fluorine-containing benzoylurea pesticides such as fluazuron and chlorfluazuron, insecticides such as high efficiency fungicide fluazinam and fluorine-containing medicines. These agricultural chemicals take DCTF as one of raw materials, which has characteristics of high efficacy and low toxicity, and distinctive characteristics of low pollution and environmentally friendly, so DCTF is developed rapidly in more than a decade.
Preparation of DCTF mainly includes following methods: (1) taking 2-amino-5-methylpyridine as raw material, generating 2-amino-3-chloro-5-(trichloromethyl) pyridine by chlorination, obtaining 2,3-dichloro-5-(trichloromethyl) pyridine by diazotization and replacing diazo group by hydrogen in the presence of the catalyst such as Cu2Cl2, and obtaining DCTF by the reaction of 2,3-dichloro-5-(trichloromethyl) pyridine and hydrogen fluoride in the presence of the catalyst such as mercuric oxide or mercuric fluoride; (2) taking 2-chloro-5-methylpyridine as raw material, carrying out side chain chlorination under photocatalysis to obtain 2-chloro-5-(trichloromethyl) pyridine, carrying out ring chlorination to obtain 2,3-dichloro-5-(trichloromethyl) pyridine catalyzed by the catalyst such as lewis acid, and obtaining DCTF by the reaction of 2,3-dichloro-5-(trichloromethyl) pyridine and hydrogen fluoride in the presence of the catalyst such as mercuric oxide or mercuric fluoride; (3) taking 3-methylpyridine as raw material, generating 3-(trichloromethyl) pyridine by the reaction with chlorine under photocatalysis, carrying out ring chlorination to obtain 2,3-dichloro-5-(trichloromethyl) pyridine catalyzed by the catalyst lewis acid, and obtaining DCTF by the reaction of 2,3-dichloro-5-(trichloromethyl) pyridine and hydrogen fluoride in the presence of the catalyst such as mercuric oxide or mercuric fluoride; (4) taking 2-chloro-5-chloromethyl pyridine as raw material, carrying out photochlorination to generate 2-chloro-5-(trichloromethyl) pyridine, generating 2,3-dichloro-5-(trichloromethyl)pyridine by heat-chlorination catalyzed by the catalyst such as lewis acid, and obtaining DCTF by the reaction of 2,3-dichloro-5-(trichloromethyl) pyridine and hydrogen fluoride in the presence of the catalyst such as mercuric oxide or mercuric fluoride. Among these methods, the process for producing DCTF by taking 2-chloro-5-chloromethyl pyridine as raw material is more widely applied in production of DCTF due to various advantages such as low raw material cost, high reaction selectivity and good product quality.
In the process for producing DCTF by taking 2-chloro-5-chloromethyl pyridine, 3-methylpyridine or 2-chloro-5-methylpyridine as raw material, the reaction material is obtained by the reaction of 2,3-dichloro-5-(trichloromethyl) pyridine and hydrogen fluoride in the presence of the catalyst such as mercuric oxide or mercuric fluoride, the reaction material should be primarily short steamed to generate short steaming liquid containing DCTF, and DCTF product is obtained by further rectifying the obtained short steaming liquid. However, in this process, DCTF rectifying short steaming residues will be produced. Most of the substances in these rectifying short steaming residues are substituted pyridine compound containing multiple halogen atoms and their polymers in molecular structure, however, they are difficult to be harmless treated by simple incineration method due to no combustibility or low combustibility. So how to treat DCTF rectifying short steaming residues efficiently, realize separation and purification or conversion of contained substances, reduce production cost of DCTF and potential pollution and hazardous of DCTF rectifying short steaming residues on environment, and increase effective utilization of resources sufficiently have become an important task of concerns gradually in recent years.